JACK Audio Connection Kit
JACK Audio Connection Kit is a professional sound server API and pair of daemon implementations to provide real-time, low-latency connections for both audio and MIDI data between applications. JACK was developed by a community of open-source developers led by Paul Davis and has been a key piece of infrastructure and the de facto standard for professional audio software on Linux since its inception in 2002. The server is free software, licensed under GPL-2.0-or-later, while the library is licensed under LGPL-2.1-or-later.
Implementations
The JACK API is standardized by consensus, and two compatible implementations exist: jack1, which is implemented in plain C and has been in maintenance mode for a while, and jack2, a re-implementation in C++ originally led by Stéphane Letz, which introduced multi-processor scalability and support for operating systems other than Linux.JACK can be used with ALSA, PortAudio, CoreAudio, FFADO and OSS as hardware back-ends. Additionally, a dummy driver and an Audio-over-UDP driver exist. One or both implementations can run on Linux, macOS, Solaris, Windows, iOS, FreeBSD, OpenBSD and NetBSD.
The JACK API is also implemented by PipeWire for backwards compatibility as a complete drop-in replacement provider for JACK clients, mapping JACK API calls to equivalent PipeWire calls. If used as a replacement for ALSA and PulseAudio as well, it can unify the different sound servers and APIs that might be typically found on a machine, and allow better integration between different software. PipeWire also claims to add a number of features and fix a number of limitations compared to JACK. The use of PipeWire as the default implementation of JACK is the default on Fedora 34 and newer.